Introducer for Deploying a Stent Graft in a Curved Lumen and Stent Graft Therefor

ABSTRACT

A stent graft ( 18 ) for deployment in a curved lumen such as the aortic or thoracic arch ( 130 ) comprises a constraining mechanism at its proximal end. A stent ( 4′ ) provided at the proximal end of the stent graft ( 18 ) includes loops of material ( 11 ) that co-operate with restraining wires ( 42 ) that extend between a central guide wire carrier ( 24 ) and a restraining wire cannula ( 8 ). The constraining mechanism acts to maintain the proximal stent ( 4′ ) constrained at three points around its circumference at both the proximal and distal ends of the proximal stent ( 4′ ). The proximal stent ( 4′ ) is thus allowed to expand after expansion of the remainder of the stent graft ( 18 ) during deployment. In an embodiment, the constraining mechanism acts to constrain two adjacent struts of the proximal stent ( 4′ ) at three points radially therearound, at the proximal end of the stent ( 4′ ) and at the distal end of the stent ( 4′ ). The proximal stent ( 4′ ) may then overlap with the interior of an adjacent stent at an inner part ( 31 ) of a curved vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of United Kingdom patent applicationnumber 0820061.0, filed Oct. 31, 2008. This application is related toUnited Kingdom patent application number 0820066.9, filed Oct. 31, 2008.

FIELD OF THE INVENTION

The present application relates to an introducer for deploying a stentgraft within a curved lumen. It also relates to a stent graft fordeployment within a curved lumen.

BACKGROUND OF THE INVENTION

Stent grafts are used to replace or repair vessels of the body such asarteries. A stent graft is usually formed from a tubular body of abiocompatible graft material with one or more stents mounted into oronto the tubular body to provide support therefore. The stents may beballoon expandable stents or self-expanding stents.

Endovascular methods have been proposed for treatment of aneurysms ofthe aorta particularly where the aneurysm is adjacent the aortabifurcation. However, when an aneurysm occurs higher up in the aorta, inthe region of the descending aorta adjacent the aortic or thoracic archor in the ascending aorta, endovascular techniques for treating theseaneurysms are somewhat more difficult because of the tight curvature ofthe aortic or thoracic arch, the occurrence of major arteries in theregion and the proximity to the heart. Placement of a substantiallycylindrical prosthesis in such a curved region can cause problems.

Stent grafts are typically deployed using endovascular techniques on anintroduction device in which the stent graft is retained in a radiallycontracted condition by a sheath. Upon withdrawal of the sheath andrelease of any retention arrangement where provided, for example incases in which the stent graft has self-expanding stents, the stentgraft can expand under the action of the self-expanding stents towardsthe vessel walls to redefine the blood flow path. The introductiondevice is withdrawn after deployment.

Currently, stent grafts are deployed in curved lumens by causing theseto follow the curvature imparted to the introducer. However, this canresult in the stent graft not sitting properly in the blood vessel andin the lumen of the prosthesis being closed off or reduced in lumendiameter.

Furthermore, when deploying a stent graft that is substantially straightin a curved aorta there is a danger that the proximal end of the stentgraft, that is, the end nearest the heart, will not lie flat against thewalls of the aorta (i.e., the end “face” is not positionedperpendicularly to the wall of the vessel) and blood can flow underneaththe edge of the graft, particularly on the inner side of the curve ofthe aortic or thoracic arch and cause the stent graft to buckle andclose off thereby causing serious problems.

FIGS. 1 and 2 illustrate this problem. The introducer and stent graftgenerally have a substantially straight configuration but as a result oftheir pliancy are urged into a curved orientation by the walls of thelumen. However, as the stent graft is held on the introducer, whichitself tends to maintain its straightened configuration to the extentthat it keeps to the outside of the curve of the lumen, the stent graftalso tends to maintain a lesser curved configuration as it is beingdeployed. When the stent graft is released from its ties to theintroducer, it expands in a manner which continues to tend to thestraightened configuration and in particular to push the inner edge ofthe stent graft forwardly. This leads to an increased Proximal FaceAngle (PFA), that is, to an increased angle between the line formed bythe proximal end of the stent graft and the line perpendicular to thewalls of the lumen. It also leads to an increased Proximal Normal Gap(PNG), that is, a gap between the lumen wall and the proximal end of thestent on the inner part of the bend in the lumen. These are shown inFIGS. 1 and 2. The Proximal Normal Gap allows blood pressure to buildbetween the outside of the stent graft and the lumen wall, which willtend to bias this side of the stent graft inwardly into the lumen andthus towards closing of the lumen of the stent graft. Thus, the seal atthe proximal end of the stent graft may not be as effective as desired.This gap can also cause the graft material itself to flap in the fluidflow, leading to unnatural fluid flow and possible premature wear andtear of the stent graft.

US 2004/0073289 discloses a stent graft for deployment within a curvedportion of the aorta.

SUMMARY OF THE INVENTION

The subject matter of the present application seeks to provide animproved introducer and method for deploying a stent graft within acurved lumen, as well as a stent graft for deployment in a curved lumen.

In general the teachings herein relate to the placement of prostheses inthe aorta in the region known as the aortic or thoracic arch, where theaorta leaves the heart and curves in approximately a U-shape to thedescending aorta, then into the abdominal aorta and then into the lowerlimbs via the iliac arteries. The teachings herein are, however, not sorestricted and can relate to placement of prostheses within or in placeof lumens in any portion of a human or animal body, though it isparticularly relevant to curved lumens.

According to an aspect of the present invention, there is provided anintroducer for deploying a stent graft in a curved lumen, the introducerincluding: a carrier for a stent graft, which stent graft is providedwith a plurality of stents including a proximal stent at a proximal endof the stent graft; a release mechanism including a constrainingmechanism operable to maintain the proximal stent of the stent graft ina constrained configuration at at least two points during deploymentwhilst allowing at least a portion of the stent graft distal of theproximal stent to expand; wherein the constraining mechanism is operableto constrain both the proximal end and the distal end of the proximalstent at said at least two points.

This arrangement ensures that the proximal-most stent of the stent graftcan be kept constrained during deployment, allowing the rest of thestent graft to expand and permitting the proximal stent to expandthereafter, so as to enable the proximal end of the stent graft to bepositioned substantially perpendicularly to the vessel wall prior to itsexpansion. In particular, this arrangement can promote overlap of graftmaterial just distal of the distal end of the proximal stent and thus abetter curvature of the stent graft. As a result, it is possible toachieve an improved seal between the proximal stent and the vessel wall.

Thus, in an embodiment, the release mechanism is operable to enable theconstrained stent to expand so as to overlap with the interior of atleast a portion of a distally adjacent stent in the expanded portion ofthe stent graft. This helps the stent graft conform to curvedvasculature.

In a preferred embodiment, the release mechanism is operable toconstrain the proximal stent at at least two, preferably three, pointsduring deployment. In an embodiment, the at least two points aresubstantially evenly spaced radially around the proximal stent.

The release mechanism preferably includes at least one restraining wireable to hold loops of thread provided on an implantable medical deviceso as to constrain the implantable medical device to the introducer. Theat least one restraining wire is preferably located within a lumen ofthe carrier of the introducer.

The introducer may include a centre guide wire carrier provided withinthe lumen of the carrier. The carrier may be provided with a pluralityof apertures therein for receiving the loops of thread of theimplantable medical device.

The introducer preferably includes at least three restraining wires. Itmay include at least six restraining wires.

According to another aspect of the present invention, there is provideda stent graft for deployment in a curved lumen, the stent graft arrangedto be deployed by an introducer as described above, wherein the stentgraft is provided with a mechanism for allowing at least two points ofthe proximal stent to be constrained during deployment whilst a portionof the stent graft is expanded, wherein the at least two points of theproximal stent are able to be constrained at both the proximal end ofthe stent and at the distal end of the stent.

According to another aspect of the present invention, there is provideda stent graft for deployment in a curved lumen, including an element ofgraft material providing an inner lumen, a plurality of stents locatedlongitudinally along the graft element, at least one of said stentsbeing a proximal stent located at a proximal end of the stent graft, aplurality of loops of thread located at or adjacent proximal and distalends of the proximal stent and extending into the inner lumen, whereinthe plurality of loops are able to allow at least two points of theproximal stent to be constrained during deployment whilst a portion ofthe stent graft is expanded, wherein the loops provided at the at leasttwo points of the proximal stent are able constrain both the proximaland the distal ends of the stent.

As such, the stent graft can provide an improved seal at its proximalend, because the proximal stent can be located substantiallyperpendicularly to the vessel wall prior to expansion.

In a preferred embodiment, the mechanism allows the proximal stent to beconstrained at three points during deployment.

Preferably, the at least two points are substantially evenly spacedradially around the proximal stent.

Preferably the constraining mechanism is operable to constrain thedistal end of the proximal stent substantially entirely therearound.

In an embodiment, the constraining mechanism is operable to constrain atleast two adjacent struts of the proximal stent to the introducer ateach of the at least two points of the proximal stent.

The loops are preferably substantially evenly spaced around thecircumference of the proximal stent.

The portions of the loops extending into the inner lumen may be locatedat or adjacent junctions of two adjoining struts forming the proximalstent.

There may be provided a plurality of threads of material for forming theloops. There may be provided a single length of thread providing saidplurality of loops.

According to another aspect of the present invention, there is providedan assembly including an introducer for deploying a stent graft in acurved lumen, the introducer including a carrier for a stent graft,which stent graft is provided with a plurality of stents including aproximal stent at a proximal end of the stent graft; a release mechanismincluding a constraining mechanism operable to maintain the proximalstent of the stent graft in a constrained configuration at at least twopoints during deployment whilst allowing at least a portion of the stentgraft distal of the proximal stent to expand; wherein the constrainingmechanism is operable to constrain both the proximal end and the distalend of the proximal stent at said at least two points; the assemblyincluding a stent graft, the stent graft including: an element of graftmaterial providing an inner lumen, a plurality of stents locatedlongitudinally along the graft element, at least one of said stentsbeing a proximal stent located at a proximal end of the stent graft, aplurality of loops of thread located at or adjacent proximal and distalends of the proximal stent and extending into the inner lumen, whereinthe plurality of loops are able to allow at least two points of theproximal stent to be constrained during deployment whilst a portion ofthe stent graft is expanded, wherein the loops provided at the at leasttwo points of the proximal stent are able constrain both the proximaland the distal ends of the stent.

Preferably the loops are able to constrain the distal end of theproximal stent substantially entirely therearound.

In an embodiment, the mechanism includes at least one wire-receiver forco-operating with a release wire of the introducer. The wire-receivermay be a loop of material, such as a suture loop.

The term thread as used herein is intended to include any filamentarymaterial which can perform the stated function and could, for example,be of conventional suture material, a multi-filamentary structure formedof yarns for example and of a natural or synthetic material such ascotton, other biocompatible material or a polymer material such aspolyester, or a mono-filamentary structure of a natural material, otherbiocompatible material, a metal such as gold or an alloy such asNitinol.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below, by way ofexample only, with reference to the accompanying drawings, in which:

FIGS. 1 and 2 are schematic illustrations of problems with deployment ofa stent graft in a curved lumen;

FIGS. 3 and 4 show an example of an implant deployment device that canbe used with the teachings herein;

FIG. 5 shows a perspective view of an embodiment of a stent graftmounted on a deployment device;

FIG. 6 shows a top view of the stent graft and deployment device of FIG.5; FIG. 7 shows a transverse cross-section through a portion of thestent graft and deployment device of FIG. 5;

FIG. 8 shows an enlargement of a part of FIG. 7;

FIG. 9 shows a longitudinal cross-section through a portion of thedeployment device shown in FIG. 5;

FIGS. 10 to 12 illustrate deployment of the stent graft of FIG. 5;

FIG. 13 illustrates another embodiment of a stent graft;

FIG. 14 illustrates another view of the stent graft of FIG. 13;

FIG. 15 illustrates another view of the stent graft of FIG. 13; and

FIG. 16 illustrates a modified arrangement of suture threads that may beused with the stent graft of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the Figures are schematic and do not showthe various components to their actual scale. In many instances, theFigures show scaled up components to assist in understanding theirstructures and functions.

In this description, when referring to a deployment assembly, the termdistal is used to refer to an end of a component which in use isfurthest from the surgeon during the medical procedure, including withina patient. The term proximal is used to refer to an end of a componentclosest to the surgeon and in practise in or adjacent an externalmanipulation part of the deployment or treatment apparatus.

On the other hand, when referring to an implantable medical device suchas a stent or stent graft, the term proximal refers to a location whichin use is closest to the patient's heart, in the case of a vascularimplant, and the term distal refers to a location furthest from thepatient's heart.

Referring to FIGS. 3 and 4, an implant deployment device 10 includes anexternal manipulation section 12, a proximal attachment region 14 and adistal attachment region 16. The proximal attachment region 14 and thedistal attachment region 16 secure the two ends of the implant 18.During the medical procedure to deploy the implant 18, the proximal anddistal attachment regions 14 and 16 will travel through the patient'svasculature, in this example, to a desired deployment site. The externalmanipulation section 12 at the proximal end of the implant deploymentdevice 10, which is operated by a surgeon to manipulate the introducer,remains outside of the patient throughout the procedure.

The distal attachment region 16 of the implant deployment device 10includes a dilator tip 20, which is typically provided with a bore 22therein for receiving a guide wire (not shown) of conventional type. Thelongitudinal bore 22 also provides a channel for the introduction ofmedical reagents. For example, it may be desirable to supply a contrastagent to allow angiography to be performed during placement anddeployment phases of the medical procedure.

A guide wire carrier or cannula 24, conventionally made from a flexiblethin walled metal tube, is fastened to the dilator tip 20. The guidewire carrier 24 is flexible so that the implant deployment device 10 canbe advanced along a relatively tortuous vessel, such as a femoralartery, and so that the distal end of the implant deployment device 10can be longitudinally and rotationally manipulated. The guide wirecarrier 24 carries a stent 18 or other device to be implanted in thepatient. The guide wire carrier 24 extends through the implantdeployment device 10 to the manipulation section 12, terminating at aconnection device 26, in conventional manner.

The connection device 26 is designed to accept a syringe to facilitatethe introduction of reagents into the guide wire carrier 24 and for thispurpose is typically provided with a threaded luer lock connection.

Where provided, a pusher sheath or rod 30 (hereinafter referred to as apusher member), typically made from a plastics material, is mountedcoaxial with and radially outside of the guide wire carrier 24. Thepusher member 30 is “thick walled”, that is the thickness of its wall ispreferably several times greater than that of the guide wire carrier 24.In some instances, the pusher member 30 and the guide wire carrier 24are the same component, possibly having different outer diameters at thelocation at which the stent 18 is to be carried.

A sheath 32 extends coaxially over and radially outside of the pushermember 30. The pusher member 30 and the sheath 32 extend distally to themanipulation region 12.

The implant 18, which is a stent graft, is retained in a compressedcondition by the sheath 32. The sheath 32 extends proximally to a sheathmanipulator and haemostatic sealing unit 34 of the external manipulationsection 12. The haemostatic sealing unit 34 includes a haemostatic seal(not shown) and a side tube 36 held to the unit 34 by a conventionalluer lock 38.

The sheath manipulator and haemostatic sealing unit 34 also includes aclamping collar (not shown) that clamps the sheath 32 to the haemostaticseal and a silicone seal ring (not shown) that forms a haemostatic sealaround the pusher member 30. The side tube 38 facilitates theintroduction of medical fluids between the pusher member 30 and thesheath 32. Saline solution is typically used.

During assembly of the implant deployment device 10, the sheath 32 isadvanced over the proximal end of the dilator tip 20 of the proximalattachment region 16 while the implant 18 is held in a compressed stateby an external force. A suitable distal attachment (retention) section(not visible in this view) is coupled to the pusher member 30 andretains a distal end 40 of the prosthesis 18 during the procedure. Thedistal end of the prosthesis 18 may be provided with a loop of material(not shown) through which a distal restraining wire 42 extends. Thedistal restraining wire also extends through an aperture (not shown inFIGS. 1 and 2) in the proximal attachment section 40 into an annularregion 44 between the guide wire carrier 24 and the pusher member 30.The distal restraining wire 42 extends through the annular space 44 tothe manipulation region 12 and exits the annular space 44 at a distalwire release mechanism 46.

A proximal portion of the external manipulation section 12 includes atleast one restraining wire actuation section 50 mounted on a body 48, inturn mounted onto the pusher member 30. The guide wire carrier 24 passesthrough the body 48. The distal wire release mechanism 46 and theproximal wire release mechanism 50 are mounted for slidable movement onthe body 48.

Clamping screws 52 prevent inadvertent early release of the prosthesis18. A haemostatic seal (not shown) is included so that the release wirescan extend out through the body 48 without unnecessary blood loss duringthe medical procedure.

A proximal portion of the external manipulation section 12 includes apin vise 54 mounted onto the proximal end of the body 48. The pin vise54 has a screw cap 56. When screwed in, vise jaws (not shown) of the pinvise 54 clamp against or engage the guide wire carrier 24. When the visejaws are engaged, the guide wire carrier 24 can only move with the body48 and hence it can only move with the pusher member 30. With the screwcap 56 tightened, the entire assembly can be moved together as onepiece.

Once the implant deployment device 10 is in the desired deploymentposition, the sheath 32 is withdrawn and the proximal and distal wirerelease mechanisms 50, 46 are released to allow the prosthesis 18 toexpand.

For some procedures, the sheath 32 may be left in place after expansionof the implant 18. The pusher member 30 and guide wire carrier 24 may bewithdrawn and replaced by a further component, using the sheath 32 as aguide.

It is to be understood that the guide wire carrier 24 can sometimes bedescribed, both above and in the description which follows, as a centerguide wire carrier, as a cannula or as a sheath and in all of theembodiments described herein it could take any of these forms. It isalso to be understood that although some embodiments described belowmake use of a guide wire carrier as well as an introducer carrier, thisis not an essential combination as it is envisaged that in someembodiments a guide wire may be carried within the carrier of theintroducer, that is without any separate guide wire carrier or cannula.

FIGS. 5 to 7 illustrate an embodiment of stent graft 18, shown mountedon an introducer 10′, which may be of the type illustrated in FIGS. 3and 4. The stent graft 18 is formed from a tubular element ofbiocompatible graft material 1 provided with a plurality of stents 4, 4′disposed along its length, the example shown including Z-stents. In thisembodiment, the stent 4′ located at the proximal end of the tubularpiece of graft material 1 is disposed on the inside of the tube 1,whereas other stents 4 are located outside the tube 1. In otherembodiments, the various stents can be positioned differently withrespect to the inside and outside of the tube and can also be all on thesame side.

The most proximal stent 4′ is provided, at substantially equally spacedlocations therearound, with three loops of suture material 11 at itsproximal end and three loops of suture material 11 at its distal end.The loops of suture material 11 are, in this embodiment, threadedthrough the graft material 1 and around a strut of the stent 4′. Otherarrangements may be envisaged in other embodiments.

The loops of suture material 11 are able to engage with a release wire42 of the introducer 10′ to form a constraining mechanism for use duringdeployment of the stent graft 18. The constraining mechanism serves toconstrain the proximal stent 4′ on the deployment device 10′ at, in thisembodiment, three positions around its circumference, resulting in thecreation of three lobes 13 of graft material 1 at the proximal end ofthe stent graft. The purpose of this is described below.

FIGS. 8 and 9 illustrate one example of a constraining mechanism forconstraining the proximal stent 4′ of a stent graft 18 on an introducer10′. The deployment device 10′ in the region of the proximal retentionmechanism has, in this embodiment, a guide wire carrier 24 and arestraining wire carrier 8 (typically the carrier of the introducer forcarrying the medical device) located coaxially around the guide wirecarrier 24, that is such that the guide wire carrier resides in a lumenof the carrier 3 or 8. In some embodiments the guide wire may be locateddirectly in the restraining wire carrier 8, thus avoiding the need for aseparate guide wire carrier 24.

Restraining wires 42 pass along the annular space between the guide wirecarrier 24 and the restraining wire carrier 8 and exit through apertures7 at the six retention points and then re-enter the annular spacebetween the guide wire carrier 24 and the restraining wire carrier 8 andpass into the nose cone dilator 20 to be secured thereby. A guide wirepasses through the lumen of the guide wire carrier, catheter or cannula24 in conventional manner.

In this embodiment, three separate restraining wires 42 are provided.Each restraining wire 42 extends to, and acts to constrain, an alignedproximal and distal attachment point on the proximal stent 4′.

The apertures 7 may be equally spaced around the restraining wirecarrier 8 or they may be spaced at other selected spacings. In thisembodiment there are two sets of three apertures 7 spaced atapproximately 120° to each other around the circumference of and inpairs along the restraining wire carrier 8.

Where each restraining wire 42 exits out of an aperture 7, a thread ofsuture material or other thread-like material 11 is looped around therestraining wire 42 and is fastened to a bight 114 of the graft material1 of the stent graft 18 and tied off with a knot 112. The restrainingwires 42 extend to an external manipulation section 12 including arestraining wire actuation section 50, such as that illustrated in FIGS.3 and 4.

In use, in order to improve the positioning of the stent graft 18 withina curved lumen, the constraining mechanism for the proximal stent 4′ isonly released after the remainder of the stent graft 18 has beenexpanded. This is described with reference to FIGS. 10 to 12.

It can be seen that the aortic or thoracic arch 130 of aorta 25 has anouter curve 33 and an inner curve 31. A stent graft 18 is deployed intothe thoracic arch 130 to span, for instance, a tear 126 in the wall ofthe aorta 25 which has caused an aortic dissection 27.

An introducer 10′, having a stent graft 18 mounted thereon, is insertedinto the aorta 25 and curved around the thoracic arch 130 as it passesthrough this, until the stent graft 18 is located at the desired site ofdeployment. FIG. 10 shows the introducer 10′ prior to withdrawal of thesheath 32, which covers the stent graft 18. The introducer 10′ is thenoriented within the vessel, such that one of the constrained portions ofthe proximal stent 4′ is facing the inner part of the curve (as can bebest seen with reference to FIG. 11). The orienting step is carried outin a known manner using, for example, radio-opaque markers (not shown),which may be located on the stent graft 18 and/or on the deploymentdevice 10′.

The surgeon or clinician then withdraws the sheath 32 to expose thestent graft 18. The stent graft 18 is allowed to expand by means of itsself-expanding stents 4, in this embodiment, or by means of a balloonexpansion mechanism in the case of use of stents which are notself-expandable.

FIG. 11 shows the stent graft 18 after withdrawal of the sheath 32. Itcan be seen that the stent graft 18 has expanded apart from at theproximal stent 4′, which is still constrained to the introducer 10′ atthree points around its circumference at both its proximal end and itsdistal end.

For the final stage of deployment, the surgeon or clinician releases therestraining wires 42 of the constraining mechanism to allow the proximalstent 4′ to expand. The curve of the thoracic arch 130 forces theproximal stent 4′ and its adjacent stent 4 closer together at the innerpart of the curve 31. As the proximal stent 4′ expands after itsadjacent stent 4, the proximal stent 4′ overlaps with the interior ofits adjacent stent 4 at the inner part of the curve 31, forming a regionof overlap 120.

This arrangement enables the plane of the proximal stent 4′ to bepositioned substantially perpendicularly to the vessel wall prior torelease. As a result, it is possible to achieve an improved seal betweenthe proximal stent 4′ and the vessel wall. In prior art systems wherethe proximal stent is constrained only at its proximal end, the stentforms a cone shape after partial release, and is unable to be positionedperpendicularly to the vessel wall.

In this embodiment of FIGS. 5 to 12 it is important to orient the lobesof the proximal stent 4′ in order to ensure that no lobe 13 becomeslocated on the inner side of the curve of the lumen, as so doing couldprevent the stent 4′ from overlapping into the second stent 4 as it isreleased and thus prevent proper positioning of the proximal stent 4′.

The skilled person will appreciate that modifications to theabove-described embodiments may be made. In particular, the suture loops11 may be provided on the proximal stent 4′ or may be provided on thegraft material 1. The constraining mechanism may be provided by anysuitable arrangement. The above-described arrangement is merelyexemplary. In some embodiments there could be provided six restrainingwires, each able to restrain a single suture loop 114.

Another embodiment of a stent graft 18 for deployment within a curvedlumen is described with reference to FIGS. 13 to 15, which shows a stentgraft 18 having a proximal stent 4′ that is to be constrained at bothits proximal and distal ends during deployment. FIGS. 13 and 14 show theproximal stent 4′ in its partially deployed state, that is after releaseof the proximal end of the proximal stent 4′ but before its distal endhas been fully released.

As can best be seen in FIG. 13, there is provided on the stent graft 18a suture arrangement in which three suture loops 132 can be pulled intothe center of the stent graft 18, that is towards the guide wire carrier24 and held thereto by a release wire within the lumen of the guide wirecarrier 24 through a plurality of openings 7 therein. The arrangement ofsuture loops 132 differs from the arrangement of the embodimentillustrated in FIGS. 5 to 9, in that a plurality of pairs of struts ofthe proximal stent 4′ is constrained by each loop arrangement, therebypulling the entirety of the distal end of the proximal stent 4′ towardsthe guide wire carrier 24, as can be seen in FIGS. 13 and 14. It ispreferred that the proximal stent 4′ is still pulled in a tri-lobedconfiguration, as with the embodiment of FIGS. 5 to 9, but in such a waythat the entirety of the distal end of the proximal stent 4′ is pulledinwardly to some extent and thus to lie within the perimeter of thesecond stent 4 adjacent to it.

A variety of different embodiments of suture arrangements for the stentgraft 18 are possible. One embodiment is shown in FIG. 15, in whichthere are provided three lengths of suture thread 132 each attached tofour stent apices. Each suture thread 132 is located generally on theoutside of the graft material 1 apart from a length which feeds to theinside of the graft material 1, as can best be seen in FIG. 15. Thislength can be fed through an opening 7 in the guide wire carrier 24 andrestrained by a restraining wire therein, to produce the tiedarrangement shown FIG. 13. A similar arrangement is provided also at theproximal end of the proximal stent 4′ to constrain this to the guidewire carrier 24.

Although not shown in the Figures, it is preferred that threerestraining wires are provided, extending through the guide wire carrier24. Each restraining wire can then serve to engage generally alignedproximal and distal suture threads 132. It will be appreciated that theproximal and distal constraining mechanisms may be slightly off-set withrespect to one another due to the nature of the Z-stents used in thisexample.

Deployment of this embodiment is very similar to that described abovewith respect to FIGS. 10 to 12. The main difference is that orientationof the stent graft 18 with respect to the curvature of the vessel is notrequired. The reason for this is that since the entirety of thecircumference of the distal end of the proximal stent 4′ is pulledinwardly towards the carrier 3 or 24. Thus, as the stent graft isdeployed, the distal end of the proximal stent 4′ is already in partialoverlap with the second stent 4 of the stent graft and thus better ableto conform to the curvature of the vessel. This therefore rendersdeployment more straightforward.

As illustrated in FIGS. 13 and 14, it is also preferred that withdrawalof the release wires engaged with the suture threads 132, acts firstlyto release the proximal end of the proximal stent 4′ and secondly torelease the distal end of the proximal stent 4′.

It can be seen from the above that in this embodiment, the constrainingmechanism constrains the distal end of the most proximal stent 4′substantially around the entirety of its circumference yet preferablystill retaining a tri-folded configuration. As is apparent from FIG. 14,the distal end of the proximal stent 4′ lies within the circumference ofthe second stent 4 and, when deployed in a curved lumen, will expand tooverlap with the interior of the second stent 4 so as to follow moreaccurately the curvature of the lumen (aortic arch). This results in animproved fit within the patient's lumen.

Pulling the distal end of the proximal stent 4′ to the carrier 24 hasanother important advantage in that the stent graft 18 is then held tothe guide wire carrier 24 during deployment. When in the aortic arch,the introducer 10, and thus the guide wire carrier 24, will tend tofollow the outside of the curve of the aortic arch, that is, the regionof greater length. Thus, the stent graft 18 will be urged against thelumen wall at the outside of the curve with those parts at the inside ofthe curve held away from the vessel wall by being held close to theguide wire carrier 24. Thus, the portions of the stent graft 18 whichwill be positioned on the shorter part of the inside of the curve willonly come into contact with this once they are released from the guidewire carrier 24 and thus already in a curved configuration. This assistsin ensuring that the distal end of the proximal stent 4′ on the insideof the curve overlaps with the proximal end of the second stent therebyto provide good conformity with the vessel wall.

The skilled person will appreciate that there are of course manymodifications that could be made to this embodiment.

In a modification, one or more suture threads 132 may be locatedpreferably substantially entirely on the outside of the graft layer 1 inorder to minimise the amount of suture material 132 on the insidethereof which could interfere with medical devices subsequentlyintroduced through the stent graft, such as during a subsequent medicalprocedure. FIG. 16 illustrates such a modification, in which portions ofsuture thread located on the outside of the graft material are shown asa dashed line, while portions of suture thread 130 on the inside of thegraft material 1 are shown as a thicker solid line. It can be seen thatsuture material 132 is located on the inside of the graft material 1only between the struts of the proximal stent 4′, and towards the apicesthereof. In this way, the struts act to hide or shield the loops ofsuture material 132 from any later used medical device. The suturethreads 132 are thus somewhat protected by the struts of the proximalstent 4′ from snagging on a later inserted medical device.

FIG. 16 shows the use of a single length of suture material 130circumscribing the entirety of the circumference of the stent graft 1.This facilitates the manufacture of the stent graft 1 as well asfacilitating its mounting onto an introducer, in particular in caseswhere there are provided many portions 132 of suture material extendinginto the inside of the graft tube and thus each being selectively ableto be held by the constraining wires. On the other hand, there could beprovided separate lengths of suture material, as in the embodiment ofFIG. 15, but in which the portion 132 extending into the graft tube islocated between the apex (trough when viewed as in FIG. 15) of two stentstruts in order to provide the shielding described above.

In the preferred embodiment (as described above), three restrainingwires are used, one for each suture thread 132, but each engaging withboth a proximal and a distal suture thread 132. However, it is possibleto use only a single restraining wire, which engages with all threesuture threads 132, though this arrangement may interfere with theposition of the guide wire. In another modification, six restrainingwires may be used, each engaging with a single proximal or a singledistal suture thread 132. An advantage of this embodiment is that itallows improved control of release of the proximal stent 4′.

It is to be appreciated that the proximal end of the proximal stent 4′is preferably retained by a similar arrangement of suture threads 130such that when the stent graft is first deployed the proximal stent 4′is held both at its proximal and at its distal ends by the constrainingmechanisms in, preferably, a tri-lobed manner but in which the lobes donot extend beyond the diameter of the second stent 4. During deployment,once the remainder of the stent graft 1 has been deployed, the proximalend of the stent 4′ is released, allowing the proximal end to open up ina manner as shown in FIGS. 13 and 14 in particular. This allows theproximal end of the stent graft 1 to engage the walls of the patient'svessel and to be held thereto, particularly in the case where fixingbarbs are provided. Then, the distal end of the stent 4′ can bereleased, allowing this to expand and in particular allowing the distalend of the stent 4′ at the inside of the curve to expand in overlappingmanner into the second stent 4. This can ensure good curvature of thestent graft 1 particularly at its proximal end and thus betterconformity with the vessel wall and better sealing.

What has been described and illustrated herein is a preferred embodimentof the invention along with some of its variations. The terms,descriptions and figures used herein are set forth by way ofillustration only and are not meant as limitations. Those skilled in theart will recognize that many variations are possible within the spiritand scope of the invention, which is intended to be defined by thefollowing claims, and their equivalents, in which all terms are meant intheir broadest reasonable sense unless otherwise indicated.

The disclosures in United Kingdom patent application 0820061.0, fromwhich the present application claims priority, and in the abstractaccompanying this application are incorporated herein by reference.

1. An introducer for deploying a stent graft in a curved lumen, theintroducer including: a carrier for a stent graft, which stent graft isprovided with a plurality of stents including a proximal stent at aproximal end of the stent graft; a release mechanism including aconstraining mechanism operable to maintain the proximal stent of thestent graft in a constrained configuration at at least two points duringdeployment whilst allowing at least a portion of the stent graft distalof the proximal stent to expand; wherein the constraining mechanism isoperable to constrain both the proximal end and the distal end of theproximal stent at said at least two points.
 2. An introducer as claimedin claim 1, wherein the release mechanism is operable to enable theconstrained stent to expand so as to overlap with the interior of atleast a portion of a distally adjacent stent in the expanded portion ofthe stent graft.
 3. An introducer as claimed in claim 1, wherein therelease mechanism is operable to constrain the proximal stent at threepoints during deployment.
 4. An introducer as claimed in claim 1,wherein the at least two points are substantially evenly spaced radiallyaround the proximal stent.
 5. An introducer as claimed in claim 1,wherein the release mechanism includes at least one restraining wireable to hold loops of thread provided on an implantable medical deviceso as to constrain the implantable medical device to the introducer. 6.An introducer as claimed in claim 5, wherein the at least onerestraining wire is located within a lumen of the carrier of theintroducer.
 7. An introducer as claimed in claim 6, including a centreguide wire carrier provided within the lumen of the carrier.
 8. Anintroducer as claimed in claim 6, wherein the carrier is provided with aplurality of apertures therein for receiving the loops of thread of theimplantable medical device.
 9. An introducer as claimed in claim 5,including at least three restraining wires.
 10. An introducer as claimedin claim 5, including at feast six restraining wires.
 11. A stent graftfor deployment in a curved lumen, including an element of graft materialproviding an inner lumen, a plurality of stents located longitudinallyalong the graft element, at least one of said stents being a proximalstent located at a proximal end of the stent graft, a plurality of loopsof thread located at or adjacent proximal and distal ends of theproximal stent and extending into the inner lumen, wherein the pluralityof loops are able to allow at least two points of the proximal stent tobe constrained during deployment whilst a portion of the stent graft isexpanded, wherein the loops provided at the at least two points of theproximal stent are able constrain both the proximal and the distal endsof the stent.
 12. A stent graft as claimed in claim 11, wherein themechanism allows the proximal stent to be constrained at three pointsduring deployment.
 13. A stent graft as claimed in claim 11, wherein theat least two points are substantially evenly spaced radially around theproximal stent.
 14. A stent graft as claimed in claim 11, wherein theconstraining mechanism is operable to constrain the distal end of theproximal stent substantially entirely therearound.
 15. A stent graft asclaimed in claim 11, wherein the constraining mechanism is operable toconstrain two adjacent struts of the proximal stent to the introducer ateach of the at least two points of the proximal stent.
 16. A stent graftas claimed in claim 11, wherein the loops are substantially evenlyspaced around the circumference of the proximal stent.
 17. A stent graftas claimed in claim 11, wherein the portions of the loops extending intothe inner lumen are located at or adjacent junctions of two adjoiningstruts forming the proximal stent.
 18. A stent graft as claimed in claim11, wherein there are provided a plurality of threads of material forforming said loops.
 19. A stent graft as claimed in claim 11, whereinthere is provided a single length of thread providing said plurality ofloops.
 20. An assembly including an introducer for deploying a stentgraft in a curved lumen, the introducer including: a carrier for a stentgraft, which stent graft is provided with a plurality of stentsincluding a proximal stent at a proximal end of the stent graft; arelease mechanism including a constraining mechanism operable tomaintain the proximal stent of the stent graft in a constrainedconfiguration at at least two points during deployment whilst allowingat least a portion of the stent graft distal of the proximal stent toexpand; wherein the constraining mechanism is operable to constrain boththe proximal end and the distal end of the proximal stent at said atleast two points; the assembly including a stent graft, the stent graftincluding: an element of graft material providing an inner lumen, aplurality of stents located longitudinally along the graft element, atleast one of said stents being a proximal stent located at a proximalend of the stent graft, a plurality of loops of thread located at oradjacent proximal and distal ends of the proximal stent and extendinginto the inner lumen, wherein the plurality of loops are able to allowat least two points of the proximal stent to be constrained duringdeployment whilst a portion of the stent graft is expanded, wherein theloops provided at the at least two points of the proximal stent are ableconstrain both the proximal and the distal ends of the stent.
 21. Anassembly as claimed in claim 20, wherein the loops are able to constrainthe distal end of the stent substantially entirely.
 22. An introducersubstantially hereinbefore described with reference to, and asillustrated in the accompanying FIGS. 3 to
 16. 23. A stent graftsubstantially hereinbefore described with reference to, and asillustrated in the accompanying FIGS. 3 to
 16. 24. An assemblysubstantially hereinbefore described with reference to, and asillustrated in the accompanying FIGS. 3 to 16.